In application Ser. No. 905,499 filed May 12, 1978, a continuous cradle pad is disclosed which extends throughout the length of a stub sill railway tank car. A reinforcing plate and a protective skid are provided to protect a tank car lading valve for bottom unloading and/or a tank car sump for top unloading, both of which normally project below the tank bottom in excess of one (1) inch. However, this continuous cradle pad, reinforcing plate and skid add a great deal of weight to the car, and thus reduce the allowable weight for lading. Furthermore, the cost of fabricating and welding in place the continuous cradle pad, reinforcing plate and skid add considerable cost.
In U.S. Pat. No. 4,114,783 granted Sept. 19, 1978, a low profile sump is disclosed which does not extend below the tank bottom in excess of one (1) inch and thus a protective skid is not required to comply with AAR and DOT regulations concerning projections extending below the tank bottom. However, the shallow depth of this sump often makes it difficult to remove the last portion of the lading in the bottom of the tank and requires a costly telescoping siphon pipe arrangement.
In rubber lined tank cars it is desirable to utilize a siphon pipe guide, or rubber spider, positioned within the sump to prevent the siphon pipe from moving horizontally or laterally within the sump and possibly breaking off near the top of the of the tank due to metal fatigue. This rubber guide cannot fit within the low profile sump disclosed in U.S. Pat. No. 4,114,783.
In application Ser. No. 860,987 filed Dec. 15, 1977, now U.S. Pat. No. 4,184,633, a combination tank car valve seat and skid for bottom unloading is disclosed in which, in one embodiment, the skid is welded to the tank bottom.